Upgrading Oracle Grid Infrastructure 11.2 (it’s just another marketing name for the Oracle Clusterware, formerly known as Cluster Ready Services CRS) usually is easy: The runInstaller offers an upgrade mode, and discovers nodes and versions without further effort.

But what, if not? The message will be “[INS-40406] The installer detects no existing Oracle Grid Infrastructure software on the system” and runInstaller just refuses to continue.

Finally I found out, that the culprit may be in the
“$ORACLE_BASE/../oraInventory/ContentxXML/inventory.xml” file. The Clusterware home may not be flagged as CRS there (CRS=”true” missing):